This document summarizes a new well unloading solution being developed for coal seam gas wells in Fairview, Australia. The solution involves a mobile skid-mounted separator and unloading tank that can be moved between wells. It aims to reduce well pressure to atmospheric conditions to increase gas velocity and unload water from wells in a low-cost, environmentally friendly way without the need for excavation or lining. The design details and status of the project are provided, noting the concept and process designs are complete and delivery is expected by the end of 2012.

1. H a s a n S i d d i q u i a n d J u l i u s M o n i
GLNG Upstream Operations – Engineering & Planning, Santos Ltd, Brisbane, QLD 4000, Australia
W E L L U N L O A D I N G S O L U T I O N
Fairview is located in the Comet Ridge Project Area.
Sales gas production commenced in 1997, and today
production is around 130 TJ/day, with the average
well productivity at 1 TJ/day. Almost 200 wells have
been drilled to date, and these wells are in various
stages of development. Longer term, more than 4,000
wells will be required to feed gas to the LNG trains at
Gladstone.
The coal seam gas field comprises of free-flow and
pumped wells. A well consists of a separator, with
water and gas gathering lines. The gas flows to
plants where it is compressed and dehydrated, while
the water flows to treatment plants where it is treated
and recycled.
During early stages of the well production life cycle,
gas rates increase and water rates decrease. Water
production is the primary focus initially in the
dewatering phase, as it allows the gas to flow later.
Wells that are able to flow gas above a “critical
velocity” are able to lift water without intervention.
Critical velocity is defined as the minimum gas
velocity in the tubing required to move liquid droplets
up to the surface.
However some wells lose their ability to flow gas
above this “critical velocity”, for various reasons. In
these wells, water builds up in the well bore (i.e. they
load-up). As wells load-up, it causes gas flow to
decrease or cease, resulting in lost gas production.
A tell tale sign of liquid loading is a significant
differential pressure across the casing and tubing
pressures on a free flow well. This is more typical in
wells that are moving between the dewatering and
stable phases of the production lifecycle.
IntroductionIntroduction Increasing bottom hole pressure is more expensive,
as compared to decreasing the surface pressure. For
this reason, decreasing the surface pressure is the
more attractive option, and it is used in the design of
the new well unloading solution.
Additionally, by lowering the surface pressure (i.e. the
backpressure on the well) to atmospheric conditions,
the maximum gas velocity is reached through the
tubing, which creates the best conditions for lifting
water from the well bore.
The skid assembly that we are constructing is mobile
and will feature a separator that operates at
atmospheric pressure.
It is connected directly to the well head tubing
minimizing backpressure. The separator will allow all
gas to flow to the existing flare on the lease. Water
will flow into unloading tank by gravity, minimizing
environmental impact.
Upon completion of unloading a tanker will remove
the water and the equipment will be rigged down and
moved to the next candidate well.
Unloading Tank
• 220 bbls capacity with access step and platform
• Fully self contained in a single load, no crane
required for set up
• Locally built in Roma, transport dimensions are
within restrictions of length, width, height, and
weight
Design DetailsDesign Details
• Suits relatively simple needs of CSG wells
• One truck for transport within road limits
• All components are mounted on a single skid base
• All components are easily handled and assembled
by a two-person work party
• No automation is required
• Designed to eliminate working at heights issue
• Separator connection points to well and flare are
located on both sides of the skid
• Gravity flow of water from separator to tank
• Cost just under 200K, which can be recovered by
the production of one well in a year
• Will be used to do simple well tests to determine
well completion requirements, which could save
more than 200K just for one well
AdvantagesAdvantages
Project UpdateProject Update
• Concept design completed
• Process design completed
• Purchase order issued
• Separator and tank design completed
• 3D- Model completed and under review
• Drafting in progress
• Expected delivery date: End of year 2012
AcknowledgementsAcknowledgements
James Jonutis – GLNG Upstream Operations
Jessica McClintock – GLNG Upstream Operations
ReferencesReferences
James F. Lea, Henry V. Nickens, and Mike R. Wells,
Gas Well Deliquification
Separator Vessel
• 2.2 MMscf/d and 400 bwpd capacity with manway,
internal ladder, and magnetic-type level gauge
• Code & Class: AS 1210 & Class 2A
• No PSV requirement, globe valve provides
pressure control at tie-in point
Connection
to well
Connection
to well Connections
to flare
AimAim
ConceptConcept
The aim of the project is to develop a low cost
method to unload a well that provides predictable and
repeatable results in an environmentally friendly and
commercially viable way. Ideally, the new unloading
method should reduce well pressure to atmospheric,
capture water and flare dry gas, all while eliminating
the need for excavation, lining, fencing and
remediation.
In order to restore water loaded wells to gas
production, built up liquid is lifted from the well bore
by increasing the gas flow velocity in the tubing. This
can be achieved by either:
1. Increasing the bottom hole pressure by:
• Using an “air pack”; this uses a large compressor
to pump a high volume of air down the annulus
and unload the tubing against gathering system
pressure
2. Decreasing the surface pressure to atmospheric
conditions by:
• bypassing the separator to the flare stack
(banned)
• bypassing the separator to a flare pit
All the methods in the bullet points above have fewer
advantages as compared to the disadvantages.
Some of the disadvantages are: uncontrolled release
of water to grade; expensive civil work; high potential
for cold venting; expensive and unpredictable results.
When gas flow velocity from a well is not sufficient to
lift the liquids to the surface against gathering system
pressure, external intervention is needed to unload
the well. At present in Fairview 10-20% of the existing
wells require some form of treatment to unload the
well bore and reach maximum gas flow rates.
Time
R
a
t
e
Rate falling off decline
curve, indication of
loading
Declining water production curve analysis
time
dewatering stable decline
rates
Candidate CSG Wells